# Maths Problem- Need Urgent Help!!?

Hey there, i need this maths problem finished and pronto!

It is regarding proportion.

IMPORTANT- Answers should include full method working for each part of the question- clearly labelled and correct.

Here comes the question:

y is directly proportional to the square of x.

y=72 when x=2

a) Express y in terms of x

b) Work out the value of y when x=1/2.

Please remember full working all clearly labelled.

Many thanks- and be speedy!

### 7 Answers

- Anonymous1 decade agoBest Answer
First of all, if y is directly proportional to the square of x, you can write this as

y = kx^2, where k is a constant of proportionality.

Because you have been given two values, it is possible to work out the value of k.

(i've used * for multiplication to avoid confusion with x!)

72 = k * 2^2

72/4 = k

k = 18

So your answer to a is y = 18x^2

For b simply plug in 1/2 to your equation:

y = 18 * (1/2 ^2)

y = 18 * 1/4

y = 4.5

- 4 years ago
I can't answer that, because for that fraction, I don't know if the numerator is 5, (4+5), (2*4+5). Same with the denominator. However, if I assume that you mean: 2 x 4 + (5 / 2) - 3 x 4 + 3 = then follow the order of operations, PEMDAS. That stands for Parentheses, Exponents, Multiplication, Division, Addition Subtraction. Multiplication and division are done at the same time but from left to right, as are addition and subtraction. So first, you can't do anything with what is in parentheses, and there are no exponents, so start with multiplication and division: (2*4) + (5/2) -(3*4) +3 = 8 + (5/2) -12 +3 Now, add or subtract from left to right: (8 5/2) -9 convert to improper fractions with a denominator of 2: 21/2 - 18/2=3/2 So the answer is 3/2.

- 1 decade ago
Since y is proportional to x^2, call that proportion "k". Then:

y = k*x^2

If y = 72 when x = 2, plug those in to find k:

72 = k*2^2

72 = 4*k

18 = k

So the answer to part a) is y = 18*x^2

For b), just plug in 1/2 for x and solve:

y = 18*(1/2)^2

y = 18*(1/4)

y = 18/4 = 9/2 = 4.5

- Anonymous1 decade ago
To find out the proportion solve the equation

2-squared * N = 72

4N = 72

N = 18

so

Y = X-Squared * 18

When x - 1/2,

(1/2)-squared * 18 = y

1/4 * 18 = y

y = 4.5

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- momLv 71 decade ago
y is directly proportional to the square of x.

y=72 when x=2

y=kx²

72=k(4)

18=k

--------------

a) Express y in terms of x

y=18x²

-----------------

b) Work out the value of y when x=1/2.

y=18(1/4)

y=4.5

- Anonymous1 decade ago
Do your own questions!

ask sombody in person or tell the teacher you dont understand